Mystery "Check Engine" light

Please tell me you pulled the trouble codes, please? What is the point of having a computer controlled engine if you aren't going to bother to see what it has to say about the problem. The EEC IV has excellent diagnostic capabilities and even has some test routines built in. I love being able to pull codes on mine- it beats the hell out of guessing what is wrong. By running a jumper wire across two connectors under the hood you can read the blinking "check engine" light for the codes. An alternative is to go to an Auto-Zone and get free check w/ a scanner.

Your computer probably knows what is wrong, all you have to do is ask it...

JL
[addsig]

Yep, they pulled the codes. They tried everything (and I watched them do it--I didn't just take their word for it). Like I said, these guys are on the hook if the motor grenades itself, so they gave it the fine-tooth comb treatment. It came up clean. Cleaning the MAS was the last resort, and, since I had a day a week or so ago when the light mysteriously 'fixed' itself and then 'unfixed' itself, all parties concerned are convinced it's just a little short somewhere, or a false signal from the oxy sensors.
[addsig]

So what were the codes? Tell me what they were and I can tell you why your light is on. And don't tell me ther eweren't any. If the light comes on it is because a code was generated.

JL

Thanks, JL--I'll have to look it up, but it was printed out for me on the receipt. I'll get back to you and post it here, or PM you.
[addsig]

The only codes which came up are:

(igniton on, engine not running)
Manual Lever Position out of range

OR

Neutral Drive Switch failure or open circuit.

(engine running)
HEGO O2 Sensor voltage low.

And, I just double-checked these with a Innova ECM code reader.


Also, now the reader is disconnected and the car is back to normal, the 'check engine' light seems to go on/off if I rock the car with the igniton on (engine off). It's gotta be a short--what else could it be?

I forgot to mention my car does not have A/C, if that makes a difference.



_________________
"This war has nothing to do with oil, literally nothing to do with oil."--Donald Rumsfeld, on CBS Radio

<font size=-1>[ This Message was edited by: IronYuppy on 1/17/03 8:35am ]</font>

Sounds like the short or intermittent open is your neutral safety switch. Need to check the connectors going into your T5. The text for the O2 sensor does not may=tch my manual. Can you post the numeric codes?

JL
[addsig]

I guess that's why it appeared to be as simple as a short in the lightbulb--I guess even rocking the car/tranny would affect that circuit(?)-- There's a short-shift stick on the T-5 -- maybe the previous owner buggered it up. I'll check that. The code on my reader was "67", followed by the 'system pass' (111) code.

I think the code was "91" on the oxy sensor. Does that sound right?

To be safe, since those readings are two weeks old, I checked three times today, to be sure. Once with a nearly-cold car (just reaching operating temp), once with about tem minutes driving-time on it, and once after a hour-long drive at highway speeds.

As an aside--I'm really impressed that the comp is sophisticated something as simple as a neutral switch being defective. Does it make coffee, too? [img]/phpBB/images/smiles/icon_wink.gif[/img] This is the first non-warranty car I've had in a long time--this self-diagnostic technology is pretty cool!

_________________
"This war has nothing to do with oil, literally nothing to do with oil."--Donald Rumsfeld, on CBS Radio

<font size=-1>[ This Message was edited by: IronYuppy on 1/17/03 11:54am ]</font>

Then you should really like this-

Code 91, KOER: HEGO circuit indicates sytem lean (left HO2S)

C (continuous memoy): No HEGO switching detected (left HO2S)

So, sounds like the most likely reason for a code 91 is an exhaust leak on the left side or bad O2 sensor or associated wiring.

I highly recomend the following book:
"How to Understand, Service and Modify Ford Fuel Injection &amp; Electronic Engine Control" by Charles Probst. published by Bentley Publishers. $29.95 www.BentleyPublishers.com

The EECIV is a very sophisticated computer that actualy learns and adapts to changes in engine, driver and environment. With good reference info and some experience, you can troubleshoot almost any problem on the EFI 5.0 using the capabilities of the EECIV. It even has built in tests for injector operation and cylinder weakness.

JL
[addsig]

If you like I can send you a jpg of the page that shows how to test the O2 sensors. 300k.

JL

Jim--thanks loads for all the info. I'm keeping our conversation in the 'open' in case there's someone with a similar problem following along.

Anyway, the exhaust has been thoroughly checked for leaks (both sides), and nothing obvious appeared. Maybe there's a small leak somewhere, but nobody can seem to find it...

As far as the O2 Sensors, that was my first assumption. But as I mentioned earlier, they borrowed a pair of sensors from another Mustang (shop owner's wife's) they had in the shop and swapped them into my car. The readout didn't change with either set of sensors (and there was no sensor code in the donor Mustang). So, unless the second set were in exactly the same condition, that probably isn't it either.

But, yeah, I'd love to have that sensor test info--what could it hurt? Thanks again!

I'm still thinking that it's a result of running 'open' 2 1/2" pipes (no cats), creating a false condition for the O2 sensors. But, at this point, I'm very, VERY open to suggestions... [img]/phpBB/images/smiles/icon_confused.gif[/img]

I guess with the short/open circuit on the tranny, there's no way to tell exactly when the check light would come on strictly because of the sensors, or if at all. Maybe I'll get onto that tranny switch tomorrow...

Thanks for the book link--I'll order a copy. I'm in the middle of "How to Win Friends and Influence People" at the moment, but as soon as I finish it, I'll move on to your suggestion, as it's probably more useful for me [img]/phpBB/images/smiles/icon_lol.gif[/img]

_________________
"This war has nothing to do with oil, literally nothing to do with oil."--Donald Rumsfeld, on CBS Radio

<font size=-1>[ This Message was edited by: IronYuppy on 1/17/03 1:37pm ]</font>